1. Field of the Invention
This invention relates to the preparation of polyisocyanurate insulating foams, and is more particularly concerned with a surfactant for the preparation of such foams from compositions containing blowing agents used to replace the conventional fully halogenated chlorofluorocarbons.
2. Description of the Prior Art
It is well known in the manufacture of rigid polyurethane and polyisocyanurate foams to employ chlorofluorocarbons, such as trichlorofluoromethane, as the blowing agent. These chlorofluorocarbon compounds boil or exhibit a significant vapor pressure at ambient temperatures and are volatilized during the exothermic reaction of an isocyanate with an active hydrogen-containing compound, such as a polyol. The expanding gas is entrapped within the reaction mixture and forms an insulating cellular structure. While the foam industry has had good results using the conventional chlorofluorocarbon blowing agents, such as CFC-11, the agents have come under attack in recent years on the ground that they are believed to give rise to environmental problems concerned with ozone depletion in the stratosphere. Accordingly, the search is ongoing for alternative blowing agents with a low ozone depletion factor to replace the conventional ones.
It is believed that hydrogenated CFC's (also known as HCFC's), which are partially halo-substituted hydrocarbons, present less risk than the CFC's. Because the HCFC's contain one or more hydrogen atoms, they more readily dissociate under conditions encountered in the atmosphere, and therefore, less of them would reach the ozone layer of the stratosphere in a form which could cause significant damage. Accordingly, the hydrogen-containing halocarbons have been investigated as possible alternatives for CFC-11 in rigid foam applications.
The search for acceptable alternative blowing agents among hydrogenated CFC's is complicated by the combination of characteristics desired in the foaming operation and finished foam products. Desirable properties include resistance to unacceptable fire or toxicological risks, good compatibility and flowability of the foam-forming components, and low friability and high strength, dimensional stability, facer adhesion, closed-cell content, and thermal insulation value of the foam product. A significant disadvantage of replacing the CFC-11 gas contained within the cells of the foam by the alternative agents is a frequent loss in the initial and aged thermal insulation performance of the foam. If polyisocyanurate foams made with the alternative agents are to remain commercially attractive and be able to comply with various national standards relating to energy consumption, it is important that such foams possess thermal insulation properties which are as close as possible to those of the foams produced with CFC-11.
There still remains a need for a rigid polyisocyanurate foam which has superior properties even though the conventional CFC blowing agents are avoided in its production.